This application claims the priority of Korean Patent Application No. 2003-39377, filed on Jun. 18, 2003, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.
1. Field of the Invention
The present invention relates to a wireless communication transmission/reception system for ultra-wideband (UWB) wireless communication environments, and more particularly to a transmission/reception system and a transmission/reception signal processing method therefor which use noncoherent modulation/demodulation techniques in UWB wireless communication environments.
2. Description of the Related Art
In wireless communication environments using a wide frequency band such as UWB (3.1˜10.6 GHz), there is the UWB signal band approach using the entire frequency band as one band and the UWB multi-band approach using subbands by dividing the entire frequency band into the limited number of subbands, and as for the time domain, continuous waveforms having a signal in all the time domain are not used, but waveforms having a signal at certain time intervals are used.
Due to such signal characteristics, mainly used for the UWB communications is the pulse position modulation (PPM) detecting in which a signal exists in a time slot of prescribed time slots and the phase shift keying (PSK) modulation using signal phase information.
FIG. 1 is a view for explaining the pulse position modulation (PPM).
As shown in FIG. 1(a), a signal becomes different depending upon in which time slot the signal exists. That is, a receiver demodulates a reception signal into “0” if the signal exists in the first time slot, and into “1” if the signal exists in the second time slot as its decision result.
As above, one of the most important factors in the pulse position modulation is the time synchronization upon implementation. A very precise time synchronization is most important to obtain an absolutely precise signal position.
In particular, in case that a narrow wave pulse (referred to as a wavelet, hereinafter) of a few hundred psec˜a few nsec is used for communications as in the UWB system, considerable difficulties are accompanied in the precise time synchronization of a few tens of pico seconds (psec).
Further, in case that pulses repeatedly appear in the same period, as shown in (b) of FIG. 1, large spikes are generated at every frequency corresponding to the reverse number of a pulse period. Accordingly, if the pulse position modulation is used, a circuit is needed to improve the spike magnitudes through the pseudo random time hopping sequence as shown in (c) of FIG. 1, which causes the entire reception system to become more complex.
In the meantime, if the phase shift keying (PSK) modulation is used, essentially needed is a time synchronization circuit having a high time resolution ability in order to find out precise phase information and a circuit for predicting a precise channel. Further, the use of a pulse having a very short time width makes it difficult to obtain multi-level phase information over the Quadrature PSK (QPSK). Accordingly, the amount of information a pulse can carry becomes small.
As above, of communication methods using signal phases, there is the Differential PSK (DPSK) performing noncoherent communications in use of relative phases to previous signals without finding out the absolute phase in time. The noncoherent DPSK system has slightly deteriorated functions compared to a coherent receiver, but has a relatively simple and easy-to-implement advantage.
FIG. 2 is a view for explaining the Differential Phase Shit Keying (DPSK) modulation.
The (a) of FIG. 2 is a view for showing a demodulator of a receiver for demodulating a DPSK-modulated reception signal. As shown in (b) of FIG. 2, the demodulator delays a signal R(t) received at t=0 by a symbol period T. The demodulator compares phases of a current reception signal R(t) and the T-delayed signal R(t+T) as a reference signal, and determines its output signal. For example, the demodulator demodulates the current reception signal into “0” if in phase, and into “1” if out of phase.
The noncoherent DPSK modulation as above has an easy-to-achieve advantage, but, in general, such noncoherent modulation is not used for UWB communications. This is because there exists a problem in that the noncoherent modulation needs the required energy per bit (Eb/No) about 3 dB higher for signal receptions compared to the coherent modulation so that communication performances are deteriorated.